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Z. Li, N.U Pucher, K. Cicha, J. Torgersen, S. Ligon, A. Ajami, W. Husinsky, A. Rosspeintner, E. Vauthey, S. Naumov, T. Scherzer, J. Stampfl, R. Liska:
"Straightforward Synthesis and Structure-Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization";
Macromolecules, 46 (2013), 2; 352 - 361.

The development of practical two-photon absorption photoinitiators
(TPA PIs) has been slow due to their complicated syntheses often reliant on expensive
catalysts. These shortcomings have been a critical obstruction for further advances in
the promising field of two-photon-induced photopolymerization (TPIP) technology.
This paper describes a series of linear and cyclic benzylidene ketone-based two-photon
initiators containing double bonds and dialkylamino groups synthesized in one step via
classical aldol condensation reactions. Systematic investigations of structure−activity
relationships were conducted via quantum-chemical calculations and experimental tests.
These results showed that the size of the central ring significantly affected the excited
state energetics and emission quantum yields as well as the two-photon initiation
efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much
broader ideal processing windows than its counterparts with a central five-membered
ring and previously described highly active TPA PIs. Surprisingly, a writing speed as
high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These
highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis
combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization.

http://dx.doi.org/10.1021/ma301770a